1. Field of the Invention
The present invention relates to an air cleaner suitable mainly for use in combination of an engine mounted on a straddle-type vehicle such as a straddle-type four-wheel vehicle or a motorcycle.
2. Description of the Related Art
FIG. 10 shows a known air cleaner 100 for a vehicle (JP-A 2003-286916). The air cleaner 100 has a cleaner case 101 formed by joining together an upper case member 102 and a lower case member 103. A support wall 104 having the shape of a deformed cylinder is formed on the bottom wall 103a of the lower case member 103. A filter assembly 105 including a cleaner element 106 is supported on the support wall 104. An air intake port 110 is formed integrally with the side wall of the lower case member 103. An air outlet port 111 to be connected to an air intake pipe of a carburetor is formed on the bottom wall 103a of the lower case member 103.
The filter assembly 105 has a lower holder 112, an upper holder 113 and a top lid 114 formed integrally with the upper holder 113. The cleaner element 106 having the shape of a deformed cylinder is put on the outside of the upper holder 113.
The support wall 104 has the shape of a deformed cylinder similar to the shape of the cleaner element 106 as shown in FIG. 11 in a plan view. The support wall 104 is formed in a fixed height H1 from the bottom wall 103a as shown in FIG. 10 and extends from a position near the air intake port 110 to a position opposite to the position of the air intake port 110. Therefore, the lower end surface of the filter assembly 105 is at a fixed height H2 from the bottom wall 103a and hence the lower end surface of the filter assembly 105 is substantially parallel to the bottom wall 103a. 
The support wall 104 is formed in the lowest possible height H1 to form the air cleaner 100 in the lowest possible vertical dimension and to form the cleaner case 101 in a volume capable of holding the cleaner element 106 having a large filtration area.
A deflecting wall 119 is disposed opposite to the inlet of the air intake port 110 to avoid induced air taken through the air intake port 110 into the cleaner case 101 directly and locally impinging on a front part of the cleaner element 106. The deflecting wall 119 separates water and mud from the induced air to prevent clogging the cleaner element 106.
In the air cleaner 100 shown in FIG. 10, the deflecting wall 119 changes the flowing direction of the induced air sharply upward so that the induced air may flow into a space over the filter assembly 105. Then, the induced air spreads into a space surrounding the cleaner element 106 and penetrates the cleaner element 106.
FIG. 12 shows another air cleaner for a vehicle (JP-A 2001-221113). A cleaner case 201 has a bottom wall 201a and a high, cylindrical support wall 202 formed integrally with the bottom wall 201a. A flat cleaner element 203 is supported on the support wall 202. The outside of the support wall 202 is opposed to an air inlet 205. Induced air impinges on a front end part of the support wall 202. The support wall separates water and mud from the induced air and changes the flowing direction of the induced air sharply upward so that the induced air may flow into a space over the cleaner element 203. The induced air flows down through the cleaner element 203.
The cleaner case 201 shown in FIG. 12 is mounted on a straddle-type four-wheel vehicle as shown in FIG. 13. In the straddle-type four-wheel vehicle, a carburetor 211 and the cleaner case 201 are stacked on an engine 210 as shown in FIG. 13. The cleaner case 201 is disposed between a steering shaft 213 on the front side of the cleaner case 201, and a seat 215 behind the cleaner case 201. Any space for disposing a fuel tank is unavailable over the cleaner case 201 thus disposed. Therefore, the fuel tank is disposed, for example, in a rear part of a body frame and the cleaner case 201 is covered with a decorative cover 220. The opposite sides of the carburetor 211 and the cleaner case 201 are covered with side covers 222.
The air cleaner shown in FIGS. 10 and 11 and the air cleaner shown in FIG. 12 make the induced air impinge on the deflecting wall 119 and the support wall 202 and deflect the flowing direction of the induced air sharply upward. Consequently, those air cleaners increase air flow resistance and have difficulty in uniformly distributing the induced air over the surfaces of the cleaner elements. Since the deflecting wall 119 and the support wall 202 form liquid separating chambers, respectively, the cleaner cases are inevitably large. When the cleaner case is formed in a small size, the cleaner element needs to be formed in a limited size inevitably having a small filtration area. Particularly, when a flat cleaner element as shown in FIG. 12 is used, the cleaner case must be inevitably formed in a large size to use a flat cleaner element having a large filtration area because the flat cleaner element naturally has a small filtration area as compared with that of the cylindrical cleaner element as shown in FIG. 11.
When the straddle-type four-wheel vehicle is provided with the decorative cover extending over the cleaner case 201 as shown in FIG. 13, the decorative cover 220 must be opened to open the cleaner case 201 when the cleaner element held in the cleaner case 201 needs to be changed. Thus the change of the cleaner element requires much work.